In the ter­rain of the human heart, sci­en­tists tell us, at least three inde­pen­dent but inter­re­lat­ed brain sys­tems are at play, all mov­ing us in their own way. To untan­gle love’s mys­ter­ies, neu­ro­science dis­tin­guish­es between neur­al net­works for attach­ment, for care­giv­ing, and for sex. Each is fueled by a dif­fer­ing set of brain chem­i­cals and hor­mones, and each runs through a dis­parate neu­ronal cir­cuit. Each adds its own chem­i­cal spice to the many vari­eties of love.

Attach­ment deter­mines who we turn to for suc­cor; these are the peo­ple we miss the most when they are absent. Care­giv­ing gives us the urge to nur­ture the peo­ple for whom we feel most con­cern. When we are attached, we cling; when we are care­giv­ing we pro­vide. And sex is, well, sex. …

The forces of affec­tion that bind us to each oth­er pre­ced­ed the rise of the ratio­nal brain. Love’s rea­sons have always been sub­cor­ti­cal, though love’s
exe­cu­tion may require care­ful plot­ting. … The three major sys­tems for lovingâ€”attachment, care­giv­ing, and sexualityâ€”all fol­low their own com­plex rules. At a giv­en moment any one of these three can be ascendantâ€”say, as a cou­ple feels a warm togeth­er­ness, or when they cud­dle their own baby, or while they make love. When all three of these love sys­tems are oper­at­ing, they feed romance at its rich­est: a relaxed, affec­tion­ate, and sen­su­al con­nec­tion where rap­port blos­soms. …

Neu­ro­sci­en­tist Jaak Pansepp…finds a neur­al corol­lary between the dynam­ics of opi­ate addic­tion and the depen­dence on the peo­ple for whom we feel our strongest attach­ments. All pos­i­tive inter­ac­tions with peo­ple, he pro­pos­es, owe [at least] part of their plea­sure to the opi­oid sys­tem, the very cir­cuit­ry that links with hero­in and oth­er addic­tive sub­stances. … Even ani­mals, he finds, pre­fer to spend time with those in whose pres­ence they have secret­ed oxy­tocin and nat­ur­al opi­oids, which induce a relaxed serenityâ€”suggesting that these brain chem­i­cals cement our fam­i­ly ties and friend­ships as well as our love rela­tion­ships.